1. Field of the Invention
The invention relates to a coil structure, more particularly to a coil structure for a coreless motor.
2. Description of the Related Art
One type of electric motor is called “coreless motor”, the armature of which is constructed without an iron core, and is referred hereinafter as the “coreless armature”. Without the iron core, issues related to ferromagnetic saturation and iron loss are reduced in the coreless motor. In addition, the coreless motor has the advantages of being lightweight and compact in size, such that fast acceleration and low cogging torque can be achieved, making the coreless armature applicable in small and micro motor applications. The techniques for manufacturing flexible printed circuit boards can be utilized for the production of the coreless armature.
FIG. 1A and FIG. 1B respectively illustrate two types of winding arrangement for conventional coil structures, where shown in FIG. 1A is the “undulated series winding” or “spiral winding” arrangement, and shown in FIG. 1B is the “lap coil winding” arrangement. A disadvantage common to these two types of winding arrangement is that the turning points of the windings are non-effective areas (i.e., do not contribute to the operation of the coreless armature) since the electric current flowing therethrough are in opposite directions. Shown in FIG. 2 is another type of winding arrangement for the conventional coil structure, where a plurality of windings are disposed on a substrate in succession relative to one another, and are each arranged in a rectangular spiral configuration. However, this arrangement has the disadvantage that, such rectangular-shape coils have more extraneous end-windings and may result in lower contribution to the operation of the coreless armature for the same copper loss. Shown in FIG. 3 is a type of winding arrangement for the conventional coil structure similar to that shown in FIG. 2. In FIG. 3, the windings are disposed on a substrate in succession relative to one another, and are each arranged in a hexagonal spiral configuration. As compared to the rectangular spiral configuration, the end portions of the hexagonal spiral configuration are reduced in length, but non-effective areas (or blank area) are still created between the end portions of two adjacent windings since no windings are present thereat. Moreover, both the rectangular and hexagonal spiral configurations shown in FIGS. 2 and 3 are elongated configurations, an adverse consequence of which is that when both sides of the substrate is provided with the windings, large areas need to be spared in the middle of the elongated configurations in order to accommodate the provision of conductive vias that interconnect corresponding windings on both sides of the substrate, again creating wasted, i.e., non-effective, areas.
In other words, there is the need for reducing the non-effective areas in coil structures so as to enhance the electromagnetic effect thereof, to thereby enhance the overall performance of the coreless motors incorporating the coil structures.